ABSTRACT

     Silinaite, ideally NaLiSi₂O₅ · 2H₂O, is a new mineral species from the Poudrette quarry, Mont Saint-Hilaire, Quebec.  It occurs as clear tabular crystals up to 2 mm, fibrous cluster, poorly formed prismatic crystals, and chalky to earthy or pwdery patches in sodalite syenite xenoliths in the nepheline syenite.   It is associated with many rare species such as erdite, kogarkoite, tugtupite, vitusite-(C), makatite, thalcusite, chkalovite, sazhinite-(Ce), sidorenkite, revdite, rasvumite, natrophosphate and many unidentified minerals.  The mineral is brittle, colorless to white with a white streak, opaque to translucent or transparent with vitreous to earthy luster.  Cleavages {001} perfect, {010} good and {110} distinct; fracture conchoidal; Mohs hardness 4.5; D(meas.) 2.24(1), D(calc.) 2.22 and 2.23 g/cm³; non-fluorescent in ultraviolet light.  g/cm³; non-fluorescent in ultraviolet light.  Optically biaxial positive, a 1.515(1), b 1.516(1), g 1.518(1), 2V (meas.) 64(1)°, 2V(calc.) 71° (g 589nm).  Orientation:  X = b, Y & c = 16° in the acute b angle.  Nonpleochroic; strong r > v, inclined.  Silinaite is monoclinic, A2/n, a 5.061(1), b 8.334(2), c 14.383(3) Å, b 96.67(2)°, Z = 4.  The strongest eight X-ray Gandolfi diffraction lines [d in Å (I)(hkl)] are:

     The ideal chemical formula is derived from a crystal-structure analysis.  Electron-microprobe analyses gave:

     Sums 98.49, 97.52 wt.%, corresponding to (Na_0.99Ca_0.01)LiSi_2.00O₅ · 2H₂O.  The name is derived from the composition.